Silicon-on-Insulator (SOI) optical devices may include an active surface layer that includes waveguides, optical modulators, detectors, CMOS circuitry, metal leads for interfacing with external semiconductor chips, and the like. The active surface can also include photodetectors that convert the light propagating in the waveguides into electrical signals. However, while crystalline silicon is excellent for forming waveguides, silicon is a poor material for generating and absorbing light at wavelengths used for digital communication. While III-V semiconductors are better suited for photo detection and generation, these materials are expensive, their fabrication shows low yield and higher cost as compared to silicon, and, most importantly, their integration into a silicon-on-insulator photonic processing is challenging. One commonly accepted way to bypass the integration problem is by local growth of germanium on a silicon substrate. The detectors made of germanium show high responsivity, bandwidth and low signal-to-noise ratios.
As the complexity and size of communicated data increases there is an increased need for more bandwidth. This is especially true for the long-haul communication where the infrastructure is limited by the discrete number of intercontinental fibers. Though germanium optical detectors are often used for long range communications, the germanium band-gap limits available bandwidth.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.